Add Flow annotations!

.eslintrc

@@ -2,19 +2,24 @@
 extends:
   - "defaults/configurations/walmart/es6-react"
 
+parser: "babel-eslint"
+
 plugins:
   - "filenames"
+  - "babel"
+  - "flowtype"
 
 rules:
   filenames/filenames: [2, "^[a-z\\-\\.]+$"] # dash-cased filenames.
   quotes:              [2, "single"]
   spaced-comment: [2, "always"]
   indent: [2, 2, {"SwitchCase": 1}]
   jsx-quotes: [2, "prefer-single"]
-  arrow-parens: [1, "as-needed"]
+  arrow-parens: 0
   no-fallthrough: 2
   no-arrow-condition: 0
   no-confusing-arrow: [2, {"allowParens": false}]
+  flowtype/define-flow-type: warn
 
 env:
   es6: true

.flowconfig

@@ -0,0 +1,20 @@
+[ignore]
+dist/
+lib/
+.*/node_modules/fbjs/.*
+.*/__tests__/.*
+.*/__mocks__/.*
+.*/node_modules/flow-typed/src/.*
+
+[include]
+src/
+
+[libs]
+interfaces/
+node_modules/flow-typed/definitions
+
+[options]
+module.name_mapper='history\(.*\)' -> 'history'
+esproposal.class_static_fields=enable
+esproposal.class_instance_fields=enable
+suppress_comment= \\(.\\|\n\\)*\\$FlowIssue]

interfaces/history.js

@@ -0,0 +1,55 @@
+declare module 'history' {
+  declare type HistoryOptions = Object;
+
+  declare type Action = 'PUSH' | 'REPLACE' | 'POP';
+  declare type Hash = string;
+  declare type Href = string;
+  declare type Path = string;
+  declare type Pathname = string;
+  declare type Query = Object;
+  declare type Search = string;
+
+  declare type LocationKey = string;
+  declare type LocationState = ?Object;
+
+  declare type Location = {
+    pathname: Pathname;
+    search: Search;
+    query: Query;
+    state: LocationState;
+    action: Action;
+    key: LocationKey;
+  };
+
+  declare type LocationDescriptorObject = {
+    pathname: Pathname;
+    search?: Search;
+    query?: Query;
+    state?: LocationState;
+  };
+
+  declare type LocationDescriptor = LocationDescriptorObject | Path;
+
+  declare type LocationListener = (location: Location) => void;
+
+  declare type TransitionHook = (location: Location, callback: ?Function) => any;
+
+  declare type History = {
+    listenBefore: (hook: TransitionHook) => Function,
+    listen: (listener: LocationListener) => Function,
+    transitionTo: (location: Location) => void,
+    push: (location: LocationDescriptor) => void,
+    replace: (location: LocationDescriptor) => void,
+    go: (n: number) => void,
+    goBack: () => void,
+    goForward: () => void,
+    createKey: () => LocationKey,
+    createPath: (location: LocationDescriptor) => Path,
+    createHref: (location: LocationDescriptor) => Href,
+    createLocation: (location: LocationDescriptor, action: ?Action, key: ?LocationKey) => Location
+  };
+
+  declare type BeforeUnloadHook = () => ?string;
+  declare type CreateHistory = (options: ?HistoryOptions) => History;
+  declare type CreateHistoryEnhancer = (createHistory: CreateHistory) => CreateHistory;
+}

package.json

@@ -16,7 +16,7 @@
     "watch-lib": "watch 'npm run build-lib' src/ -d",
     "clean": "npm run clean-lib && npm run clean-dist",
     "build": "npm run build-lib && npm run build-dist",
-    "lint": "eslint --color --ext .js,.jsx src test",
+    "lint": "concurrently 'eslint --color --ext .js,.jsx src test' 'flow check'",
     "test": "mocha test/.setup.js test/**/*.spec.js",
     "test-cov": "BABEL_ENV=coverage nyc mocha test/.setup.js 'test/**/*.spec.js'",
     "check": "npm run lint && npm run test",
@@ -61,8 +61,12 @@
     "enzyme": "^2.4.1",
     "eslint": "^3.0.1",
     "eslint-config-defaults": "^10.0.0-alpha.1",
+    "eslint-plugin-babel": "^3.3.0",
     "eslint-plugin-filenames": "0.2.0",
+    "eslint-plugin-flowtype": "^2.6.3",
     "eslint-plugin-react": "^5.2.2",
+    "flow-bin": "^0.30.0",
+    "flow-typed": "^2.0.0-beta.6",
     "jsdom": "^9.4.1",
     "lodash": "^4.13.1",
     "mocha": "^2.5.3",

src/action-types.js

@@ -1,3 +1,4 @@
+// @flow
 export const LOCATION_CHANGED = 'ROUTER_LOCATION_CHANGED';
 export const PUSH = 'ROUTER_PUSH';
 export const REPLACE = 'ROUTER_REPLACE';

src/create-matcher.js

@@ -1,30 +1,29 @@
+// @flow
 import UrlPattern from 'url-pattern';
 
-export default routes => {
-  const routeDictionary = Object.keys(routes).map(route => ({
+export default (routes: Object) => {
+  const routeList = Object.keys(routes).map(route => ({
     route,
     pattern: new UrlPattern(route),
     result: routes[route]
   }));
 
-  return incomingUrl => {
+  return (incomingUrl: string) => {
     // Discard query strings
     const route = incomingUrl.split('?')[0]; // eslint-disable-line no-magic-numbers
 
     // Find the route that matches the URL
-    for (const key in routeDictionary) {
-      if (routeDictionary.hasOwnProperty(key)) {
-        const storedRoute = routeDictionary[key];
-        const match = storedRoute.pattern.match(route);
+    for (let i = 0; i < routeList.length; i++) {
+      const storedRoute = routeList[i];
+      const match = storedRoute.pattern.match(route);
 
-        if (match) {
-          // Return the matched params and user-defined result object
-          return {
-            route: storedRoute.route,
-            params: match,
-            result: storedRoute.result
-          };
-        }
+      if (match) {
+        // Return the matched params and user-defined result object
+        return {
+          route: storedRoute.route,
+          params: match,
+          result: storedRoute.result
+        };
       }
     }
 

src/fragment.js

@@ -1,6 +1,22 @@
+// @flow
+import type { Location } from 'history';
+import type { RouterContext } from './provider';
+
 import React, { PropTypes } from 'react';
 
-const Fragment = (props, context) => {
+type Props = {
+  forRoute: string,
+  forRoutes: [string],
+  withConditions: (location: Location) => bool,
+  children: ReactPropTypes.node
+};
+
+const Fragment = (
+  props: Props,
+  context: {
+    router: RouterContext
+  }
+) => {
   const { forRoute, forRoutes, withConditions, children } = props;
   const { store } = context.router;
   const { matchRoute } = store;
@@ -30,13 +46,6 @@ const Fragment = (props, context) => {
   return <div>{children}</div>;
 };
 
-Fragment.propTypes = {
-  forRoute: PropTypes.string,
-  forRoutes: PropTypes.arrayOf(PropTypes.string),
-  withConditions: PropTypes.func,
-  children: PropTypes.node
-};
-
 Fragment.contextTypes = {
   router: PropTypes.object
 };

src/index.js

@@ -1,3 +1,4 @@
+// @flow
 import createStoreWithRouter, {
   locationDidChange,
   initializeCurrentLocation

src/initial-router-state.js

@@ -1,11 +1,24 @@
+// @flow
+import type {
+  Query,
+  History
+} from 'history';
+
 import createMatcher from './create-matcher';
 
+type Args = {
+  pathname: string,
+  query: Query,
+  routes: {[key: string]: Object},
+  history: History
+};
+
 export default ({
   pathname = '/',
   query = {},
   routes,
   history
-}) => ({
+}: Args) => ({
   ...history.createLocation({
     pathname,
     query

src/link.js

@@ -1,7 +1,20 @@
+// @flow
+import type { LocationDescriptor } from 'history';
+import type { RouterContext } from './provider';
 import React, { Component, PropTypes } from 'react';
 
 import { PUSH, REPLACE } from './action-types';
 
+type Props = {
+  href: string | LocationDescriptor,
+  replaceState: bool,
+  persistQuery: bool,
+  target: string,
+  className: string,
+  style: Object,
+  children: ReactPropTypes.node
+};
+
 const LEFT_MOUSE_BUTTON = 0;
 
 const normalizeHref = location =>
@@ -61,7 +74,12 @@ const onClick = ({e, target, location, replaceState, router}) => {
   }
 };
 
-const Link = (props, context) => {
+const Link = (
+  props: Props,
+  context: {
+    router: RouterContext
+  }
+) => {
   const {
     href,
     target,
@@ -100,16 +118,6 @@ const Link = (props, context) => {
   );
 };
 
-Link.propTypes = {
-  href: PropTypes.oneOfType([PropTypes.string, PropTypes.object]),
-  replaceState: PropTypes.bool,
-  persistQuery: PropTypes.bool,
-  target: PropTypes.string,
-  className: PropTypes.string,
-  style: PropTypes.object,
-  children: PropTypes.node
-};
-
 Link.contextTypes = {
   router: PropTypes.object
 };

src/provider.js

@@ -1,7 +1,19 @@
+// @flow
+import type { Store } from 'redux';
+
 import React, { Component, PropTypes } from 'react';
 
+export type RouterContext = { store: Store };
+
+type Props = {
+  store: Object,
+  children: ReactPropTypes.node
+};
+
 export class RouterProvider extends Component {
-  constructor(props) {
+  router: { store: Store };
+
+  constructor(props: Props) {
     super(props);
     this.router = {
       store: props.store
@@ -23,12 +35,12 @@ RouterProvider.childContextTypes = {
   router: PropTypes.object
 };
 
-RouterProvider.propTypes = {
-  children: PropTypes.node,
-  store: PropTypes.object
+type ProvideRouterArgs = {
+  store: Object
 };
 
-export default ({ store }) => ComposedComponent => props =>
-  <RouterProvider store={store}>
-    <ComposedComponent {...props} />
-  </RouterProvider>;
+export default ({ store }: ProvideRouterArgs) =>
+  (ComposedComponent: ReactClass<*>) => (props: Object) =>
+    <RouterProvider store={store}>
+      <ComposedComponent {...props} />
+    </RouterProvider>;

src/reducer.js

@@ -1,6 +1,9 @@
+// @flow
+import type { Action } from 'redux';
+import type { Location } from 'history';
 import { LOCATION_CHANGED } from './action-types';
 
-export default (state = {}, action) => {
+export default (state: ?Location | Object = {}, action: Action) => {
   if (action.type === LOCATION_CHANGED) {
     // No-op the initial route action
     if (state && state.pathname === action.payload.pathname) {
@@ -9,7 +12,7 @@ export default (state = {}, action) => {
 
     return {
       ...action.payload,
-      previous: state.current
+      previous: state && state.current
     };
   }
   return state;